Hard magnetic steel and methods of making such steel



Patented 15, was

HARD MAGNETIC STEEL AND METHODS OF MAKING SUCH S'lllElElL Walter E. Remmers, Western Springs, 111., assign or to Western Electric Gompany, Incorporated, New York, N. iii, a corporation of New York No Drawing. Application December 1, 1934, Serial No. 755,632

Claims.

This invention relates to hard magnetic steel and methods of making such steel and more particularly to cobalt steel and methodsof making cobalt steel.

Objects of the invention are to provide ferromagnetic material having good magnetic properties and effective andefiicient methods of making such material.

In accordance with one embodiment of the invention, nitrogen is passed through a molten charge of cobalt steel to improve its magnetic properties.

The type of ferro-magnetic'materials to which this invention particularly relates is cobalt magnet steel which usually contains cobalt from 5% to 40%, carbon from .4% to 1.25%, manganese from .1% to 2.5%, silicon .05% to 1.5%, chromium from 1.5% to 10.0%, tungsten 1.5% to 10.0%, and. the balance iron. These percentages refer to the more commonly used cobalt steels for permanent magnets; however, the invention is applicable to permanent magnetic cobalt steel including other ingredients and proportions.

In the manufacture of cobalt steel in accordance with this invention, a furnace, such as an -arc furnace, may be charged with the proper proportions of scrap steel, cobalt and a high carbon iron, such as washed metal, and the charge melted. Ferro-chromium, ferro-manganese, ferro-silicon, and ferro-tungsten are then added to the charge in proportions determined by the character of the scrap steel and the composition of the final product desired. The charge is melted under a suitable slag covering. When the charge and the alloy additions are molten, nitrogen is bubbled through the molten charge. The nitrogen may be passed into the charge through an iron pipe and since this pipe will tend to melt away, allowance for the amount of iron thus added may be madein compounding the alloy.

The nitrogen thus added forms nitrides with the constituents of the steel which on solidification form fine precipitates of nitrides, particularly iron and chromium nitrides. It appears that the nitrides increase the coercive force of the steel due to the distortion of the fundamental space lattice of the steel, which is of the body centered cubic type, without causing the lattice to change to some other system of crystallization.

The nitrogen is taken up by the molten charge rather slowly and, therefore, the nitrogen may be supplied for a considerable time, for instance,

55 from ten minutes to an hour orlonger. This period is given merely as an illustration and. shorter or longer periods may be used; in fact the nitrogen may be applied until the charge becomes saturated.

Nitrogen may also'be added by the addition of 5 nitrogen bearing compounds, such as nitrogen bearing ferro-chromium, in which the nitrogen is present in the form of iron and chromium nitride.

The molten steel after having been thus treated 0 is usually cast into ingots which are rolled into bars for magnets or the magnets may be cast directly. After the bars are formed or the magnets are cast, they are heated to a temperature which may range from 1500 F. to 1800 F., from which the material is quenched, preferably in oil. Due to the wide temperature range in which this steel may be heat treated, it is less critical and results in a more uniform product.

The coercive force of hard magnetic alloys may 20 also be improved by nitriding the alloys in solid form by heat treating the material in a nitrogenous atmosphere, such as ammonium gas. In this case it is preferable to apply the process for a longer period in order to obtain good penetra- 25 tion. Magnets treated in this manner have shown a marked increase in coercive force. This treatment may be in addition to the nitriding of the alloy in the molten state or it may be used exclusively of the latter. 30

While the theory above presented is believed to be correct, it is to be understood that the invention is not limited to any particular theory regarding the metallurgical changes which are responsible for the increased magnetic properties. 35

It will be understood that the embodiment of the invention herein described is merely illustrative and that many changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of making cobalt steel which comprises compounding a molten charge having from 5% to 40% cobalt, .4% to 1.25% carbon, .05% to 1.5% silicon, .1% to 2.5% manganese, 1.5% to 45 10% chromium, 1.5% to 10% tungsten, and the balance substantially iron, nitriding the steel in the molten state and quenching the steal from a temperature range of 1500 F. to 1800 F. to develop its magnetic properties.

2. A method of making cobalt steel which comprises compounding a molten charge having from 5% to 40% cobalt, .4% to 1.25% carbon, .05% to 1.5% silicon, .1% to 2.5% manganese, 1.5% to 10% chromium, 1.5% to 10% tungsten, and the balance substantially iron, passing nitrogen through the molten bath, and quenching the steel from a temperature range of 1500 F. to 1800 F. to develop its magnetic properties.

3. A method of making cobalt steel which comprises compounding a molten charge having from 5% to 40% cobalt, .4% to 1.25% carbon, .05% to 1.5% silicon, .1% to 2.5% manganese, 1.5% to 10% chromium, 1.5% to 10% tungsten, and the balance substantially iron, adding nitrogen to the molten bath of the steel, casting the molten steel into ingots, rolling. the ingots in the bars, and quenching the bars from a temperature range of 1500" F. to 1800 F. to develop their magnetic properties.

4. Cobalt steel comprising from 5% to 40% cobalt, .4% to 1.25% carbon, .05% to 1.5% silicon, .1% to 2.5% manganese, 1.5% to 10% chrobalt steel comprising from 5% to 40% cobalt, .4%

to 1.25% carbon, .05% to 1.5% silicon, .1% to 2.5% manganese, 1.5% to 10% chromium, 1.5% to 10% tungsten, an amount of nitrogen that would result from passing nitrogen gas through the molten alloy for a period of at least ten 15 minutes, and the balance substantially iron.

WALTER E. REMMERS. 

